There are a number of things to consider when looking up the sales prices of domain names, and if you’ve found a domain sale that has meaning to you, you still need to investigate a little more to find out why. Did the domain have any page rank? did it have traffic? did it actually sell? Unfortunately, the latter is a genuine concern when using Namebio to look up domain sales.
It seems that Namebio does not always record actual sales. When Namebio reports a sale from Namejet, they don’t take into account that Namejet assigns a reserve price to the choice domains that delete or expire, and they record whatever the final price was for the auction.
Take Police.net as an example, the last bidder on the domain gave up at $7500, leaving the Namejet reserve price at $7600, which is what it closed at, and so the Reserve won the auction. There was no actual sale.
Since it can not be determined after the fact that the domain actually sold unless you want to go one step further and use domain tools to research each domain sale to see if ownership changed, then it might not be out of line to assume that the price you find on Namebio is an accurate representation of aftermarket interest in the domain name.
However in the context of reporting the price under the guise of a domain sale can bring with it assumptions that can effect your pricing strategy, for good or bad, and so each example should be considered carefully.